1. Field of the Invention
The present invention relates to a sheet aligning mechanism that aligns sheets discharged into a tray, a stacker that includes the sheet aligning mechanism and sequentially stacks sheets discharged from a sheet discharging unit into an elevatable shift tray, an image forming apparatus and an image forming system including the stacker.
2. Description of the Related Art
Some image forming apparatuses, such as a copier and a printer, is provided with a stacker, which is a type of post-processing apparatus, that stacks a large number of sheets of ordinary paper or the like discharged from the image forming apparatus into an elevatable shift tray.
Some type of the stacker includes a sheet aligning mechanism that aligns sheets stacked on the shift tray in a sheet width direction (direction perpendicular to a sheet discharge direction). For example, a stacker that includes a jogger that aligns an outer side in the sheet width direction of sheets and a leading-end stopper that aligns side ends, which are ends in the sheet discharge direction, of the sheets is disclosed in Japanese Patent Application Laid-open No. 2003-312930 and Japanese Patent Application Laid-open No. 2003-312931.
However, the conventional stacker is disadvantageous in requiring space to prevent, when a sheet is picked up from sheets stacked in a shift tray, the stacked sheets from coming into contact with the jogger and thereby going out of alignment. The space has conventionally been provided only by lowering the shift tray.
To provide the space, it has been necessary to set a relatively large lowering distance for the shift tray, which entails reduction in the number of sheets that can be loaded on the shift tray, upsizing of an apparatus so as not to reduce the number of sheets that can be loaded, or placing a limit on the height of a transport unit arranged above a loading portion of the shift tray. This makes removal of a jammed sheet less easy or requires additional space only for use in the sheet removal rather than sheet stacking.